1. Field of the Invention
The present invention relates to a multichip module having an electric chip and an optical chip for performing increased transmission speed of information signals, and a method of manufacturing the multichip module. Also, the present invention relates to a multichip unit equipped with the multichip module and having an optical transmission line adapted to interconnect optical chips within the multichip module, and a method for manufacturing the multichip unit.
2. Description of the Related Art
In recent years, performance of microprocessors and capacity of memory chips have been sharply increasing with increasing operation speed and integration level of integrated circuits, thanks to technological advancements in integrated circuit chips such as IC (Integrated Circuit) chips and LSI (Large Scale Integration) chips. With the above integrated circuit chips mounted on a circuit substrate, inter-chip transmission of information including relatively short distance-transmission is performed using an electric signal.
As for further increasing performance of the integrated circuit chips, transmission speed of a signal exchanged between the chips needs to be increased, with demands for increased density of the electric signal, in other words, an electric interconnect.
However, in the circuit substrate, there is a limit for electric interconnect density, and signal delay caused by a CR (Capacitance-Resistance) time constant of the electric interconnect becomes an issue for consideration. In addition, in the circuit substrate, increasing speed of the electric signal and/or increasing density of the electric interconnect leads to development of unacceptable conditions such as EMI (Electromagnetic Interference) noise and inter-channel cross talk, for instance, so that measures against these inconvenient conditions are also necessary.
As one of approaches to settlement of the above problems, there is proposed a technology, which permits that an optical interconnect such as photo signal interconnect and optical interconnection is adapted to inter-electronic appliance, inter-circuit substrate, and inter-chip connections and so on. In particular, short-distance transmission such as inter-chip transmission of information requires that an optical transmission/communication system is configured with an optical wave-guide, which is effective in propagation of light due to total reflection, as a transmission line by forming the optical wave-guide between the chips mounted to the circuit substrate.
Thus-configured optical transmission/communication system employs a multichip unit having a circuit substrate or the like mounted with chips such as an optical chip having a light emitting section for converting an electric signal into a photo signal and/or a photo detecting section for converting the photo signal into the electric signal; and an electric chip such as IC chip and LSI chip adaptable to electric signal processing such as operational processing.
A hybrid circuit substrate having not only the above optical wave-guide but also a patterned interconnect or the like on the circuit substrate is to be employed for the multichip unit, because of needs for feed of power to the optical chip and the electric chip and/or various control signal transmission with the electric signal, for instance.
Specifically, the multichip unit employs a hybrid circuit substrate having the patterned interconnect deposited on a surface of a silicon or glass substrate using a thin film deposition technology or the like, with the optical wave-guide thereon as an optical interconnect, for instance. Alternatively, a different type of hybrid circuit substrate such as one having the optical wave-guide as the optical interconnect on a surface of an existing printed circuit board is also available. In the above hybrid circuit substrate, the optical wave-guide configured as the optical interconnect is to be formed using a low-temperature process with a polymer compound as an optical wave-guide material, for instance.
In the multichip unit, the optical chip for converting the electric signal inputted to or outputted from the electric chip into the photo signal is required for inter-packaged electric chip transmission of information with the optical interconnect. Specifically, the multichip unit requires an optical chip having, at an output side of the electric signal from the electric chip, a light emitting device such as a semiconductor laser and a light emitting diode for converting an outputted electric signal into the photo signal to emit light as the photo signal and/or an optical chip having, at an input side of the electric signal to the electric chip, a photo detecting device such as a photo detector for detecting the photo signal having been passed through the optical interconnect to convert thus-detected photo signal into the electric signal.
Specifically, in the multichip unit, the electric signal from the electric chip is applied to the light emitting device to ensure that the light emitting device converts the applied electric signal into the photo signal for emission of light, which is then allowed to propagate through the optical wave-guide or the like. Then, the photo signal having been passed through the optical wave-guide or the like is detected by the photo detecting device to ensure that the photo detecting device converts the detected photo signal into the electric signal, which is then allowed to enter the electric chip.